170 Miscellaneous Intelligence, 



battery might be retained, constantly charged to a state of ten- 

 sion, which might be heightened at pleasure, by increasing the 

 number of plates. 



M. Zamboni thinks that a pile of 50,000 pairs of plates, of 

 the usual diameter of leaves of tinned paper, would be a con- 

 stant source of electricity, of which the tension would equal that 

 of a strong common electric machine. He promises that such 

 an instrument shall be constructed, and mentions many inte- 

 resting experiments to which it may be applied. — Ann. de Chim. 

 xxix. 198. 



2. Neiv Galvanometer, by Nobili. — The construction of this 

 instrument is founded upon the fact discovered by (Ersted, the 

 deviation of a magnetic needle by a wire conveying a current of 

 electricity ; and as in most other instruments of this kind, the 

 wire is passed several times round the frame, within which the 

 needle is suspended, that the effect may be proportionally increased. 

 It differs, however, from all made before it, in the use of two 

 needles instead of one ; these are equal in size, parallel to each 

 other, magnetized in opposite directions, and fixed on a straw, 

 so that the contrary ends of the two needles point in the same 

 direction. Their distance from each other on the straw is regu- 

 lated by the construction of the frame with its covering wire, in 

 and about which they are to move. The frame of M. Nobili is 

 twenty-two lines long, twelve wide, and six high. The wire is 

 of copper covered with silk, it is one-fifth of a line in thickness, 

 from twenty-nine to thirty feet long. It makes seventy-two re- 

 volutions about the frame. The needles are twenty-two lines 

 long, three lines wide, a quarter of a line thick, and they are 

 placed on the straw five lines apart from each other. An aper- 

 ture is made in the tissue formed by the turns of the wire on the 

 upper surface of the galvanometer, by thrusting them from the 

 middle towards each side ; the lower needle on the straw is intro- 

 duced through this aperture into the interior, in consequence of 

 which the upper needle remains a little above the upper surface 

 of the wire. The aperture is retained open to a certain extent, 

 to allow freedom of motion to the needles and straw, these being 

 suspended in the usual way from the upper extremity of the straw. 

 The graduated circle on which the deviation is measured is placed 

 over the wire on the upper surface of the frame having an aper- 

 ture in its centre for the free passage of the needle and straw. 

 The upper needle is the index, the lower being visible only from 

 the sides of the instrument. 



The sensibility of this instrument depends upon the addition 

 of the upper needle. Being magnetized in an opposite direction to 

 the lower one, it almost entirely neutralizes the influence of ter- 

 restrial magnetism, leaving only so much of directive power as 



